#include<bits/stdc++.h>
using namespace std;
int main() {
  int m,n;
  int Case=0;
  while(scanf("%d%d",&n, &m)==2 && m && n) {
    double ans=0.0;
    for(;n<=m;++n) {
      ans+=1.0/((double)n*(double)n);
    }
    if(Case) puts("");
    // puts() will append a <CR> at the end of the string.
    printf("Case %d: %.5lf\n",++Case, ans);
  }
  return 0;
}
